Packaging Machine For Producing Shrinkable Packages

ABSTRACT

The invention relates to a packaging machine comprising a device for producing a deep-drawn plastic packaging tray and a welding device for welding a top foil to a packaging tray, wherein at least the packaging tray is made from a shrinkable plastic foil. A method for producing packages with the aid of at least one shrinkable foil is also disclosed.

The present invention relates to a packaging machine having a device for producing a thermoformed plastic packaging tray and a sealing device for sealing an upper film onto the packaging tray, at least, the packaging tray being produced from a shrinkable plastic film, and to a method for producing packages with at least one shrink film.

Nowadays, food is increasingly frequently offered in plastic packages, with a packaging tray in which the items of food are placed, and an upper film, with which the packaging tray is closed. The packaging trays are generally produced by thermoforming from a planar film web. In the case of some packages, either the film web into which the packaging tray has been molded and/or the upper film is what is known as a shrink film, i.e. a film which shrinks under the effect of temperature. These packages have the advantage that the packed food is very closely enclosed by the package. In the case of these packages, the upper film is first joined to the film web from which the packaging tray has been thermoformed before the shrinking is performed. In the past, the packaging trays have often shrunk back in an uncontrolled manner and/or the shrinking has already been activated by the sealing mold, with the result that the shrinking has usually been uncontrolled.

It was therefore the object of the present invention to provide a packaging machine with which the problems of the present, state of the art can be overcome.

The object is achieved by a packaging machine with a device for producing thermoformed packaging trays from a shrinkable film web with a thermoforming mold, the thermoforming mold being cooled during the thermoforming, and with a sealing device for sealing an upper film onto a packaging tray, at least the packaging tray being produced from a shrinkable plastic film, with a lower mold and an upper mold, the lower mold and/or the upper mold being cooled.

It was extremely surprising and unexpected for a person skilled in the art that such a packaging machine allows packaging trays with straight package edges to be produced from a shrinkable plastic, film and/or that the unwanted reverse shrinkage of the produced packaging tray immediately after the thermoforming is at least reduced. This allows packaging containers with an entirely new appearance and a very reproducible size to be produced. Furthermore, it was extremely surprising and unexpected that the sealing device of the packaging machine according to the invention succeeds in avoiding uncontrolled shrinkage of the packaging tray or the upper film during sealing. The packaging machine according to the invention can be produced and operated easily and at low cost.

For the purposes of the invention, a shrinkable film is a thermoformable multilayer film with a heat shrinkability in the longitudinal and transverse directions of respectively at least 20%, the heat shrinkability not being substantially influenced by thermoforming. With preference, the heat shrinkability of the multilayer films according to the invention in the longitudinal and transverse directions is respectively at least 25%, with more preference at least 30%, with still more preference at least 35%, with greatest preference at least 40% and in particular at least 45%. Such films are disclosed for example in DE 10 2005 017 937.1, which is hereby introduced as a reference and is consequently considered to be part of the disclosure.

According to the invention, the packaging machine has a thermoforming mold, which is cooled during the thermoforming. The thermoforming mold preferably has cooling means for this. Such cooling means may be, for example, cooling lines which are arranged in the region of the thermoforming mold and through which a cooling medium, for example a cooling liquid or a cooling gas, circulates.

The thermoforming device preferably has holding means, so that the film can be clamped between the holding means and the thermoforming mold. The holding means is preferably a clamping frame. The holding means is preferably arranged such that it is vertically displaceable. The film web is preferably fixed by the holding means before the thermoforming is performed. In a preferred embodiment of the present invention, this holding means is likewise provided with a cooling means, which may be connected to the same coolant circuit as the thermoforming mold or to another cooling circuit. Suitable in particular as coolant is water or a coolant that is also used for example in refrigerators and the like. This preferred embodiment of the present invention has the advantage that the region of the packaging tray to which a cover film is sealed in a further method step does not have any stresses, or only very low stresses, which results in fewer leaks in the region of the sealed seam.

At least one coolant circuit is preferably regulated, for example temperature-regulated, so that the thermoforming mold and/or the holding means is/are always at a virtually constant temperature.

Furthermore, with preference, the thermoforming device has a heating means, with particular preference a heating plate, with which the film web can be heated up, in particular before the thermoforming. With the heating means, the film web is heated at least in certain regions up to the plastifying temperature. The heating is preferably performed very quickly. With particular preference, the thermoforming device has means with which the contact, and consequently heat transfer, between the film web and the heating means is improved. With particular preference, this contact is improved by negative and/or positive pressure, which sucks and/or presses the film web onto the heating means. For the case in which a number of packaging trays are produced simultaneously, the device according to the invention preferably has a heating means for each packaging tray to be produced. The heating means are preferably vertically displaceable, can be switched on and off and/or can be regulated in their temperature. Once the film web has been heated, and with particular preference before the thermoforming, the heating means is again removed from the film web and/or switched off, in order to avoid overheating of the film web and in order to avoid too much heat having to be removed in the cooling of the thermoforming mold or of the heating means. The heating means may, however, also be used as a thermoforming die. The heating is preferably performed in a locally very targeted manner and very quickly, so that only the desired regions are heated. After or during the thermoforming, the film web is then cooled down as quickly as possible, in order to avoid unwanted recovery of the thermoformed packaging trays. A person skilled in the art realizes that the heating and cooling can also be performed simultaneously, in order to avoid certain regions of the film web being heated along with it when it is being heated and/or to reduce undesired heating up of these regions and/or to avoid unwanted recovery.

In a further preferred embodiment of the present, invention, the packaging machine according to the invention has vacuum and/or pressure means, by which the film web is pressed or drawn into the thermoforming mold and is thereby given its final shape or to improve the heat transfer between the film web and the thermoforming mold. The same or other vacuum and/or pressure means may also be used for improving the contact, between the undeformed film web and the heating means.

Furthermore, the packaging machine has a sealing device. The sealing device serves for sealing an upper film onto a packaging tray, the packaging tray and/or the cover film being produced from a shrinkable film.

The packaging tray is generally molded into a film web by thermoforming. A person skilled in the art understands that the upper film that is sealed onto the packaging tray may also be thermoformed.

With the packaging machine according to the invention, packages can be produced from a shrinkable packaging tray and a shrinkable upper film. Such packages are referred to as shrink packs. The upper film may, however, also be composed of a non-shrinkable film web, for example of a foamed polyolefin or foamed polyester. Such packages are referred to as shrink plates.

The sealing device of the packaging machine according to the invention has a lower mold and an upper mold, the lower mold being located below and the upper mold above the film webs that are to be joined to one another. The lower mold and the upper mold are pressed against one another to seal the upper film to the lower film. In this case, the sealing of the two film webs to one another is performed under the influence of temperature. According to the invention, the lower mold and/or the upper mold is/are cooled. This cooling may be performed, for example, by circulation of a cooling medium through channels that are incorporated in the lower mold and/or the upper mold. Water or the media known from refrigerators is/are suitable as a cooling medium. The cooling of the upper film and/or of the packaging trays is preferably performed in such a way that no uncontrolled shrinkage of the respective film occurs, i.e. the temperature of the respective film web must never reach or exceed the temperature at which shrinkage occurs.

Preferably, at least the lower mold is vertically displaceable, with particular preference also the upper mold.

Furthermore, with preference, the upper mold or the lower mold has a sealing means, for example a sealing frame, which is heated. The heating is generally performed by electric heating. In the case of the present invention, the heating should advantageously be restricted to the sealing means, in order that unnecessary cooling of the respective mold is not needed.

A yoke sealing plate system is preferably arranged on the mold that does not have the sealing frame. The yoke sealing plate system preferably has a rubber abutment. Furthermore, with preference, the yoke sealing plate system is cooled and, with particular preference, is likewise vertically displaceable.

The upper mold is preferably arranged such that it is vertically displaceable. Furthermore, with preference, the ripper mold is cooled to avoid heating up over time and thereby causing unwanted shrinkage of the upper film. This embodiment is of advantage in particular whenever the upper film is a shrink film.

The sealing device preferably has a cooling plate, which is arranged with particular preference in the region of the upper film. This cooling plate is preferably likewise arranged such that it is vertically displaceable. In the event that the upper film is sealed to a number of packaging trays simultaneously, a cooling plate is preferably respectively arranged in the region of each packaging tray.

Any packaging machine familiar to a person skilled in the art comes into consideration as the packaging machine. It is preferably what is known as a form-fill-seal packaging machine.

The present invention also relates to a method for producing shrinkable thermoformed packages from a packaging tray and an upper film, at least the packaging tray being produced from a shrinkable plastic film by thermoforming, in which the film web is first partially heated up and is partially cooled before and during the thermoforming and in which the upper film and/or the packaging tray is/are cooled during the sealing of an upper film onto the packaging tray.

The present invention also relates to a method for sealing packages that are produced from at least one shrink film, in which the introduction of heat for the sealing is performed from the side of the package that is facing away from the shrink film. In the case of this method according to the invention, the introduction of sealing heat is preferably performed from below or from above.

The following comments apply to both methods according to the invention.

It was extremely surprising and unexpected for a person skilled in the art that such a method allows packaging trays with straight package edges to be produced and/or that no unwanted shrinkage takes place after the thermoforming. This allows packaging containers with an entirely new appearance and a very reproducible size to be produced. The methods according to the invention prevent unwanted shrinking of the shrink film from being initiated by the sealing mold.

The film web is preferably clamped before the thermoforming. The clamping of the film web is preferably performed with a clamping frame. With particular preference, this clamping frame is cooled and, with most preference, is arranged such that it is vertically displaceable. A cooled clamping frame has the advantage that the later sealing region is at least virtually free from stress, which leads to fewer leaks in the sealing region.

Furthermore, with preference, the film web is heated up before the thermoforming. The heating up and cooling are preferably performed at different times, the heating up preferably being performed before the cooling. Furthermore, with preference, one surface of the film web is heated up and the opposite surface is cooled. In a further preferred embodiment of the present invention, the heating and cooling are performed simultaneously, the film web being heated up and cooled down in certain regions. With particular preference, the film web is pressed or sucked in the direction of the heating or cooling means, in order to achieve a heat transfer that is as good as possible. In the event that a number of packaging trays are produced simultaneously, each packaging tray to be produced is preferably assigned a heating means. This allows the required heat to be introduced into the film web in a locally very targeted manner.

The thermoforming may be performed in any way with which a person skilled in the art is familiar. However, the thermoforming is preferably performed by positive and/or negative pressure (vacuum). Furthermore, with preference, the thermoforming is performed with a die or the thermoforming is assisted by a die, it being possible for the die and the heating means to be one component.

According to the invention, the film web is cooled, at least in certain regions, before, during and/or after the thermoforming. In particular the region that has been thermoformed is cooled during and/or after the thermoforming until there is no longer any unwanted recovery of the thermoformed region. This is generally at temperatures below the plastifying temperature of the respective film.

The sealing mold that is facing the shrink film is preferably cooled. This embodiment of the method according to the invention has the advantage that the mold facing the shrink film does not unwantedly activate shrinking of the shrink film. When two shrinkable films are used, preferably both molds are cooled.

Preferably, at least the shrinkable film web is fixed before and/or during the sealing. The fixing is preferably performed with the sealing molds. Furthermore, with preference, the fixing of the shrinkable film web is performed with the chains by which the film web is transported along the packaging machine.

The invention is explained below on the basis of FIGS. 1 to 9. These explanations are given merely by way of example and do not restrict the general concept, of the invention. The explanations apply equally to the device according to the invention, the package according to the invention and the method according to the invention.

FIG. 1 shows the thermoforming device before the thermoforming.

FIG. 2 shows the heating of the film web.

FIG. 3 shows the thermoforming of the packaging tray.

FIG. 4 shows the releasing of the holding means.

FIG. 5 shows the resulting packaging tray.

FIG. 6 shows the thermoforming device.

FIG. 7 shows the sealing device.

FIG. 8 shows a packaging machine for producing a shrink plate.

FIG. 9 shows a packaging machine for producing a shrink pack.

Represented in FIG. 1 is the thermoforming device, which has a thermoforming mold 3 with a number of thermoforming chambers 10. According to the invention, this thermoforming mold is cooled, the cooling being performed in the present case by bore 2, through which a cooling medium is passed. Above the thermoforming mold 3 is the film web 1 to be deformed, which is clamped between the thermoforming mold 3 and a clamping frame 4. The clamping frame 4 can likewise be cooled in the present case, by means of the bore 5, through which a coolant is passed. Above the film web 1 are heating plates 7, which can be raised and lowered, as indicated by the double-headed arrows 6. A person skilled in the art knows that the thermoforming mold 3 is likewise vertically movable.

FIG. 2 shows the heating of the film web 1 clamped between the clamping frame 4 and the thermoforming mold 3. For this, the heating plates 7 are lowered, so that they are preferably in contact with the film web. The film web is heated up until it is at the desired temperature in the region of the heating plate. The heating is preferably performed in a time-controlled manner.

As soon as the film has been sufficiently heated, the heating plates are raised again and the thermoforming of the film web 1 for producing the vacuum trays 8 is performed (FIG. 3). In the present case, the thermoforming chambers 10 can be subjected to a vacuum, by which the film web is deformed in the way represented. During the entire heating-up and thermoforming process, the thermoforming mold and the clamping frame are cooled.

As soon as the packaging trays 8 are thermoformed (FIG. 4), the thermoforming mold 3 is lowered, so that the packaging trays 8 come out of the thermoforming mold 3. The thermoforming mold is lowered to the extent that the produced packaging trays can be transported out from the thermoforming region and renewed deforming of the film web 1 can be performed.

Represented in FIG. 5 are the finished packaging trays. The cooling of the thermoforming mold has the effect that the pack edges 9 and/or the bottom of the package are straight, because the film web does not shrink at all after the thermoforming, or shrinks only very little after or during the thermoforming.

FIG. 6 shows the thermoforming device for producing thermoformed plastic packaging trays from shrinkable films of a shrinkable film web. The device 12 has a lower mold 3 and an upper mold 19. The lower mold 3 comprises the negative of the shape of the packaging tray to be produced. Incorporated in the lower mold are channels 2, through which a coolant by which the lower mold is cooled is circulated. As indicated by the double-headed arrow, the lower mold can be lowered and raised. The film web (not presented) runs between the lower mold and the upper mold. The upper mold 19 can likewise be raised and lowered. The same applies to the clamping frame 4 and the heating means 7. With the clamping frame, the film web is pressed against the lower mold and firmly clamped, in order that it can be thermoformed. The clamping frame 4 also additionally has channels 2, through which a coolant is circulated, so that the frame of the clamping frame 4 can be cooled. The cooling of the clamping frame has the advantage in particular that the film web that is located under the clamping frame is not heated and is consequently free from stress. The upper film is later sealed onto this region. The fact that this region is free from stress has the effect that the sealing of the later resulting package has a very high level of impermeability. The device according to the invention has a heating element 7 for each packaging tray to be produced. With these heating elements, the film web is heated as quickly as possible. In order to improve the heat transfer between the film web and the respective heating means, a positive pressure may be produced in the region under the film web, pressing the film web against the heating means and thereby improving the heat transfer. A person skilled in the art recognizes that a negative pressure may also be produced between the film web and the heating means 7, sucking the film web against the heating means. As soon as the film web has reached its plastifying temperature, it is pressed into the respective thermoforming mold by the heating means 7, which then acts at the same time as a die, and/or a negative pressure is established in the thermoforming mold, sucking the film web into the thermoforming mold. This thermoforming mold is cooled, so that the film web is cooled during and/or immediately after the thermoforming. This cooling is performed until the film web has reached a temperature at which unwanted recovery of the packaging tray on account of the shrinkability of the film can be ruled out.

FIG. 7 shows the sealing device 13 according to the invention, which comprises an upper mold 6 and a lower mold 3. The sealing device is part of a packaging machine. Arranged between the upper mold and the lower mold are the upper film 14 (not represented) and the shrinkable film web 1 (not represented), in which packaging trays 8 have been incorporated by thermoforming. In the present case, the upper film 14 is likewise shrinkable. The film web 1 is fixed and transported by two chains (not represented) in a packaging machine (not represented). The upper film 14 is sealed onto the film web 1 in order to close the packaging trays 8. The upper film 14 is fixed by chains or the like and is transported in a known way by being joined to the lower film 1. As represented by the double-headed arrow, the upper mold is vertically displaceable. Arranged on the upper mold is the heated sealing frame 4, which is pressed against the yoke sealing plate system 5 during the sealing. As a result, the film webs 1, 14 are pressed against one another. The pressure thereby produced and the increased temperature have the effect that the upper film is sealed onto the edge of the packaging trays 8. Arranged on the upper mold in the region of each packaging tray is a cooling plate 2, which prevents the upper film from heating up outside the sealing. This embodiment is of interest in particular in the case of shrinkable upper films. The cooling plates 2 are likewise vertically displaceable. The lower mold is also vertically displaceable, as indicated by the double-headed arrow. In the present case, the lower mold is also cooled in order to prevent unwanted shrinking of the packaging tray during the sealing. For the case where the upper film is not shrinkable, it is generally possible to dispense with the cooling plate 2 and cooling of the upper mold 6.

FIG. 8 shows a packaging machine for producing a shrink plate, i.e. a package with a shrinkable packaging tray, which is closed by a non-shrinkable, comparatively rigid cover film. A film web is unrolled intermittently from a roll 11 and packaging trays 8 are molded into the film web in the thermoforming device 12. These packaging trays 8 are then filled with an item to be packed (not represented) and after that closed with a cover film 14 in the sealing station 13. In the present case, the film web 11 comprises a shrinkable film while the film web 14 is non-shrinkable and relatively rigid, so that, it acts like a tray. After the sealing, the packaging tray is shrunk in a shrinking device 15, only the thermoformed packaging tray coming into contact with a hot medium, for example hot air, steam or water. The shrunk packages completed in this way are then individually separated by the cutting device 16 and transported away as finished package 17. The respective double-headed arrows show that one or two units of the respective station can be raised and lowered.

FIG. 9 shows a packaging machine for producing a shrink pack in two views. A shrink pack comprises a shrinkable upper film and a shrinkable lower film. Once again, the shrinkable film web is unrolled from a roll 11 and the packaging trays 8 are molded into the film web by thermoforming in a forming station 12. Once the packaging trays have been filled with an item to be packed (not represented), the packaging tray is closed by sealing with a film web 14 in the sealing station 13. In the present case, the cover film is likewise a shrinkable film. In a next method step, the packaging is individually separated in a cutting station 16. The packages 18 produced in this way are shrunk in a shrinking tunnel, in which they are subjected to boiling water from all sides. The respective double-headed arrows show that one or two units of the respective station can be raised and lowered.

LIST OF DESIGNATIONS

-   1 film web -   2 cooling means, cooling plate -   3 lower mold, thermoforming mold -   4 sealing frame, holding means, clamping means -   5 yoke sealing plate system, cooling means -   6 upper mold, bottom of the packaging tray, double-headed arrow -   7 heating means, heating plates, heating element, heating cartridge -   8 packaging tray -   9 pack edges -   10 pack bottom -   11 roll of film -   12 thermoforming station -   13 sealing station, sealing device -   14 upper film -   15 shrinking station, shrinking tunnel -   16 cutting station -   17 finished, shrunk package -   18 package before shrinking -   19 upper mold 

1. A packaging machine for producing a package with a thermoforming mold for producing thermoformed packaging trays from a shrinkable film web and with a sealing device with a lower mold and an upper mold for sealing a shrinkable upper film onto the packaging trays, characterized in that the thermoforming mold is cooled during the thermoforming and the lower mold and/or the upper mold are cooled during the sealing.
 2. The packaging machine as claimed in claim 1, characterized in that the lower mold has a cooling means.
 3. The packaging machine as claimed in claim 1, characterized in that the lower mold is vertically displaceable.
 4. The packaging machine as claimed in claim 1, characterized in that it has sealing means, which are heatable.
 5. The packaging machine as claimed in claim 1, characterized in that the upper mold has a cooling plate.
 6. The packaging machine as claimed in claim 5, characterized in that the upper mold has a cooling plate for each package to be produced.
 7. The packaging machine as claimed in claim 1, characterized in that the upper mold and/or the cooling plates is/are arranged such that they are vertically displaceable.
 8. The packaging machine as claimed in claim 1 one, characterized in that it has a yoke sealing plate system, which is preferably arranged on the lower mold.
 9. The packaging machine as claimed in claim 8, characterized in that the yoke sealing plate system is cooled.
 10. The packaging machine as claimed in claim 8, characterized in that the yoke sealing plate system can be raised and lowered.
 11. The packaging machine as claimed in claim 8, characterized in that the yoke plate sealing system has a rubber abutment.
 12. The packaging machine as claimed in claim 1, characterized in that the thermoforming mold has cooling means.
 13. The packaging machine as claimed in claim 1, characterized in that the film web can be clamped between a holding means and the thermoforming mold.
 14. The packaging machine as claimed in claim 13, characterized in that the holding means can be cooled by cooling means.
 15. The packaging machine as claimed in claim 1, characterized in that the holding means is arranged such that it is vertically displaceable.
 16. The packaging machine as claimed in claim 1, characterized in that the thermoforming mold has a heating means, with which the film web can be heated up.
 17. The packaging machine as claimed in claim 16, characterized in that the heating plate is configured as a thermoforming die.
 18. The packaging machine as claimed in claim 1, characterized in that the thermoforming mold has vacuum and/or pressure means for thermoforming the film web.
 19. The packaging machine as claimed in claim 1, characterized in that the thermoforming mold has the vacuum and/or pressure means to improve the contact between the film web and the heating means.
 20. A method for producing a package by sealing an upper film onto a packaging tray, at least the packaging tray being produced from a shrinkable plastic film, characterized in that the film web is first partially heated up and is partially cooled before and during the thermoforming and in that the upper film and/or the packaging tray is cooled during the sealing of the upper film onto the packaging tray.
 21. The method as claimed in claim 20, the packaging tray and/or the upper film being produced from a shrink film, characterized in that the introduction of heat for the sealing is performed from the side of the package that is facing away from the shrink film.
 22. The method as claimed in claim 20, characterized in that the introduction of heat for the sealing is performed from above.
 23. The method as claimed in claim 20, characterized in that the shrinkable plastic film is preferably fixed by the sealing molds.
 24. The method as claimed in claim 20, characterized in that the shrinkable plastic film is fixed by the transporting chains.
 25. The method as claimed in claim 20, characterized in that the sealing mold that is facing the shrinkable plastic film is cooled.
 26. The method as claimed in claim 20, characterized in that the shrinkable plastic film is thermoformed before the sealing.
 27. The method as claimed in claim 20, characterized in that the package is shrunk after the sealing.
 28. The method as claimed in claim 20, characterized in that the film web is first partially heated up and is partially cooled before and during the thermoforming.
 29. The method as claimed in claim 20, characterized in that the film web is clamped before the thermoforming.
 30. The method as claimed in claim 20, characterized in that the packaging tray has a sealing region and in that this sealing region is cooled during the heating up and/or during the thermoforming.
 31. The method as claimed in claim 20, characterized in that the film web is deformed by positive and/or negative pressure.
 32. The method as claimed in claim 20, characterized in that each packaging tray is assigned a heating means.
 33. The method as claimed in claim 20, characterized in that the thermoformed film is cooled until there is no recovery.
 34. The packaging machine as claimed in claim 9, characterized in that the yoke sealing plate system can be raised and lowered.
 35. The packaging machine as claimed in claim 4, characterized in that the film web can be clamped between a holding means and the thermoforming mold.
 36. The packaging machine as claimed in claim 7, characterized in that the film web can be clamped between a holding means and the thermoforming mold.
 37. The packaging machine as claimed in claim 35, characterized in that the holding means can be cooled by cooling means.
 38. The packaging machine as claimed in claim 14, characterized in that the holding means is arranged such that it is vertically displaceable. 